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Coil size/ shape as it relates to depth
- Thread starter B sperty
- Start date
LongRanger
New member
Be sperty
I was given an older SSP 2000pi,by an elderly friend. I re-configured the 40X40" coil to a 52X56" semi-round. I really had no choice,as the old pvc tubing,was pretty much shot. I set it up with a balancing handle,so that I can use it from a position out-side the coil. For the same length of coil-wire,I have a coil that is 52X56". It's my belief that round is the most efficient...but,an elliptical covers a wider area,as one sweeps. I'm not 100% on this,but,I think that an 8" coil,will go as deep as an 8X10" coil. Hope this answers some questions...
David
I was given an older SSP 2000pi,by an elderly friend. I re-configured the 40X40" coil to a 52X56" semi-round. I really had no choice,as the old pvc tubing,was pretty much shot. I set it up with a balancing handle,so that I can use it from a position out-side the coil. For the same length of coil-wire,I have a coil that is 52X56". It's my belief that round is the most efficient...but,an elliptical covers a wider area,as one sweeps. I'm not 100% on this,but,I think that an 8" coil,will go as deep as an 8X10" coil. Hope this answers some questions...
David
LongRanger
New member
B sperty
I was given an older SSP 2000pi,by an elderly friend. I re-configured the 40X40" coil to a 52X56" semi-round. I really had no choice,as the old pvc tubing,was pretty much shot. I set it up with a balancing handle,so that I can use it from a position out-side the coil. For the same length of coil-wire,I have a coil that is 52X56". It's my belief that round is the most efficient...but,an elliptical covers a wider area,as one sweeps. I'm not 100% on this,but,I think that an 8" coil,will go as deep as an 8X10" coil. Hope this answers some questions...
David
I was given an older SSP 2000pi,by an elderly friend. I re-configured the 40X40" coil to a 52X56" semi-round. I really had no choice,as the old pvc tubing,was pretty much shot. I set it up with a balancing handle,so that I can use it from a position out-side the coil. For the same length of coil-wire,I have a coil that is 52X56". It's my belief that round is the most efficient...but,an elliptical covers a wider area,as one sweeps. I'm not 100% on this,but,I think that an 8" coil,will go as deep as an 8X10" coil. Hope this answers some questions...
David
Here is some info posted by Eric Foster many years ago that might help.
"Here are the curves I have used for many years. As Robert said, the range reaches a maximum when it is equal to the radius of the coil. Coils larger or smaller than this optimum will result in less range. To show how this works, along the bottom axis you see coil diameter, which is obviously 2 x the radius. So for an 11in coil, if we go up the vertical scale to A, we have 5.5in. Also note the diagonal line and the series of ever increasing semicircles. Everything to the left of this line shows increasing detection range up to the maximum where it intersects the line, then decreasing range to the right, where the semicircles are shown dashed.
If a certain metal object is just detected at 5.5in with the 11in coil, then going larger in coil size will cause a reduction (going down the dashed side), and going smaller in coil size will have a similar effect. Initially, it won
"Here are the curves I have used for many years. As Robert said, the range reaches a maximum when it is equal to the radius of the coil. Coils larger or smaller than this optimum will result in less range. To show how this works, along the bottom axis you see coil diameter, which is obviously 2 x the radius. So for an 11in coil, if we go up the vertical scale to A, we have 5.5in. Also note the diagonal line and the series of ever increasing semicircles. Everything to the left of this line shows increasing detection range up to the maximum where it intersects the line, then decreasing range to the right, where the semicircles are shown dashed.
If a certain metal object is just detected at 5.5in with the 11in coil, then going larger in coil size will cause a reduction (going down the dashed side), and going smaller in coil size will have a similar effect. Initially, it won
verylazybeachbum
New member
B sperty, which pulse are you using, or contemplating using?
Also what is your target? rings, coins, nuggets, etc.
When i had a Minelab GPX-4000, all research and experimentation pointed to the 14 round mono being the best for depth on average rings and coins. Whatever you did, you would never want to go over 18" diameter for your average targets, because of power limitations. You would gain little depth but loose sensitivity to smaller objects. I experimented with coils ranging from 8.5 -24 inches. If its nuggets your after the 14" would probably be on the extreme high end of your range. There are bigger nuggets that can be picked up deeper by bigger coils but that would be digging some pretty deep holes for a long shot, most nuggets (in the US anyway are small).
I am now primarily beach detecting with High Powered Pulsepower units which should be on the same power level as the GPX units, although the GPX might have a little more power. Let me say that I could not get any of my Minelab coils to work well with my Pulsepower Goldscan 5c(TDI), and always went back to the stock 11" made by Eric Foster. If you want a larger coil for the TDI or Goldscan I would get one made for those machines. Eric made a 15" mono for some of the Deepstar machines but they were rare. If I was going to get a larger coil it would be 14-15" round Mono, for Beach work anyway. But the 11" stock coil works so well so far I have not worried too much about it.
Also what is your target? rings, coins, nuggets, etc.
When i had a Minelab GPX-4000, all research and experimentation pointed to the 14 round mono being the best for depth on average rings and coins. Whatever you did, you would never want to go over 18" diameter for your average targets, because of power limitations. You would gain little depth but loose sensitivity to smaller objects. I experimented with coils ranging from 8.5 -24 inches. If its nuggets your after the 14" would probably be on the extreme high end of your range. There are bigger nuggets that can be picked up deeper by bigger coils but that would be digging some pretty deep holes for a long shot, most nuggets (in the US anyway are small).
I am now primarily beach detecting with High Powered Pulsepower units which should be on the same power level as the GPX units, although the GPX might have a little more power. Let me say that I could not get any of my Minelab coils to work well with my Pulsepower Goldscan 5c(TDI), and always went back to the stock 11" made by Eric Foster. If you want a larger coil for the TDI or Goldscan I would get one made for those machines. Eric made a 15" mono for some of the Deepstar machines but they were rare. If I was going to get a larger coil it would be 14-15" round Mono, for Beach work anyway. But the 11" stock coil works so well so far I have not worried too much about it.
TheMarshall
New member
Reg said:Here is some info posted by Eric Foster many years ago that might help.
"Here are the curves I have used for many years. As Robert said, the range reaches a maximum when it is equal to the radius of the coil. Coils larger or smaller than this optimum will result in less range. To show how this works, along the bottom axis you see coil diameter, which is obviously 2 x the radius. So for an 11in coil, if we go up the vertical scale to A, we have 5.5in. Also note the diagonal line and the series of ever increasing semicircles. Everything to the left of this line shows increasing detection range up to the maximum where it intersects the line, then decreasing range to the right, where the semicircles are shown dashed.
If a certain metal object is just detected at 5.5in with the 11in coil, then going larger in coil size will cause a reduction (going down the dashed side), and going smaller in coil size will have a similar effect. Initially, it won
Hi Matt,
Personally, I have built a bunch of coils of various sizes and shapes and the fundamentals and approximate depth increases put forth by Eric Foster in his post appear to hold true within reason when checking both air and in ground tests. At least they do for the basic tests I have run. That is why I posted the information. I will agree that there are a wealth of variables that can influence the final result so there are no absolutes. I believe even Eric would agree and mentioned some of the factors in his response.
I don't believe Eric ever meant this information to be the gospel but I believe he felt the concept does give some form of a reference point of what one might expect and that is, what I believe was the fundamental basis of the answer to the the question that was asked.
Ironically, one other person who had a wealth of knowledge came to the same basic design answers as Eric Foster and that was Robert Hooko, another well known Electrical Enginner and contributor to this forum. Much of his work can also be found in the archives of this forum, as can that of Eric. Unfortunately, I read that Robert died some time back so he will not be responding with his explanation as to why he came to similar mathimatical conclusions.
Of course, most people who read this forum realize that Eric has retired and may not respond either.
There will always be absolutes that probably should be introduced for the purist that just may influence or vary from the graphs, but to try to include all of them would require developing a book that most likely couldn't be read properly by the average user. That is, why I feel Eric added the possible variables he did in his response.
You are certainly welcome to provide your own chart and other technical specifics contradicting Eric's work if you feel I am wrong in supporting Eric's findings, as I always am looking for technical information. But, as I mentioned, as a general rule, I have found Eric's graphs to be reasonably accurate and as such I feel they do provide some simple approximate basis upon which one can make an assumption, at least for those who use one or more of many if not most of the PI's used today.
One more item and that is, as I mentioned before, even Eric agreed that there were factors that could influence the final results, especially when searching for small nuggets and again, I have found somewhat greater errors on such items. However, for more constant objects such as coins, I found the general results to accurate enough I feel one could have some idea of whether a coil of different size might thelp. Again, I say might because even the ground conditions can play a part far more than people realize. Of course, the size, shape and characteristics of the object also can influence the results. So, people should keep such in mind also and realize they will have an influence on the overall accuracy of any possible tests.
Reg
Personally, I have built a bunch of coils of various sizes and shapes and the fundamentals and approximate depth increases put forth by Eric Foster in his post appear to hold true within reason when checking both air and in ground tests. At least they do for the basic tests I have run. That is why I posted the information. I will agree that there are a wealth of variables that can influence the final result so there are no absolutes. I believe even Eric would agree and mentioned some of the factors in his response.
I don't believe Eric ever meant this information to be the gospel but I believe he felt the concept does give some form of a reference point of what one might expect and that is, what I believe was the fundamental basis of the answer to the the question that was asked.
Ironically, one other person who had a wealth of knowledge came to the same basic design answers as Eric Foster and that was Robert Hooko, another well known Electrical Enginner and contributor to this forum. Much of his work can also be found in the archives of this forum, as can that of Eric. Unfortunately, I read that Robert died some time back so he will not be responding with his explanation as to why he came to similar mathimatical conclusions.
Of course, most people who read this forum realize that Eric has retired and may not respond either.
There will always be absolutes that probably should be introduced for the purist that just may influence or vary from the graphs, but to try to include all of them would require developing a book that most likely couldn't be read properly by the average user. That is, why I feel Eric added the possible variables he did in his response.
You are certainly welcome to provide your own chart and other technical specifics contradicting Eric's work if you feel I am wrong in supporting Eric's findings, as I always am looking for technical information. But, as I mentioned, as a general rule, I have found Eric's graphs to be reasonably accurate and as such I feel they do provide some simple approximate basis upon which one can make an assumption, at least for those who use one or more of many if not most of the PI's used today.
One more item and that is, as I mentioned before, even Eric agreed that there were factors that could influence the final results, especially when searching for small nuggets and again, I have found somewhat greater errors on such items. However, for more constant objects such as coins, I found the general results to accurate enough I feel one could have some idea of whether a coil of different size might thelp. Again, I say might because even the ground conditions can play a part far more than people realize. Of course, the size, shape and characteristics of the object also can influence the results. So, people should keep such in mind also and realize they will have an influence on the overall accuracy of any possible tests.
Reg
LongRanger
New member
Hi Reg,
I have an early '90s GOLDSCAN,with the stock 11in coil. Could you give me "the values" for this machine,so I can get Lamar Cannon to help me make a fourty two inch coil for it. He does the electronics,while I do the mounting part. So far I have done a 24in square--and a 62in round,for the TDI. Both work great.
Any help would be very much appreciated...
Thanks,
David
lebarondavid@yahoo.com
I have an early '90s GOLDSCAN,with the stock 11in coil. Could you give me "the values" for this machine,so I can get Lamar Cannon to help me make a fourty two inch coil for it. He does the electronics,while I do the mounting part. So far I have done a 24in square--and a 62in round,for the TDI. Both work great.
Any help would be very much appreciated...
Thanks,
David
lebarondavid@yahoo.com
Hi David,
Basically, the coils that work on the TDI should work on the Goldscan, even the early GS models such as the GS 4. Build the coil to a 300 uh or maybe a little more, rather than slightly less and it should work ok. You can go higher in inductance just fine but the delay at which it will work will increase if you do.
I changed the coil connector on my GS 4 units to match the TDI units but one could build a simple adapter if they didn't want to change connectors. In any case, the coils you already have should work on the older GS models. Lamar should be able to figure out the turns ratio for the size coil you desire. However, my guess is the number of turns for a 42" coil will be either 8 to 10 depending upon whether the 42" measurement was for a rectangular or round size. I would probably pick the 9 to try first for the rectangular and maybe 10 for the round size.
BTW, doesn't sound like you are going to be looking for birdshot with that size coil.
Reg
Basically, the coils that work on the TDI should work on the Goldscan, even the early GS models such as the GS 4. Build the coil to a 300 uh or maybe a little more, rather than slightly less and it should work ok. You can go higher in inductance just fine but the delay at which it will work will increase if you do.
I changed the coil connector on my GS 4 units to match the TDI units but one could build a simple adapter if they didn't want to change connectors. In any case, the coils you already have should work on the older GS models. Lamar should be able to figure out the turns ratio for the size coil you desire. However, my guess is the number of turns for a 42" coil will be either 8 to 10 depending upon whether the 42" measurement was for a rectangular or round size. I would probably pick the 9 to try first for the rectangular and maybe 10 for the round size.
BTW, doesn't sound like you are going to be looking for birdshot with that size coil.
Reg
LongRanger
New member
Thanks Reg,
Well,it sounds like I need to continue building my coils for the TDI,as I have been doing--and simply build an adaptor,so that they will be inter-changable with the GoldScan.
Now the GoldScan has a three pin connector--as opposed to the TDI's five pin. Do you have any advice/information,that would help me to accomplish this task? Thanks for the help...
David
Well,it sounds like I need to continue building my coils for the TDI,as I have been doing--and simply build an adaptor,so that they will be inter-changable with the GoldScan.
Now the GoldScan has a three pin connector--as opposed to the TDI's five pin. Do you have any advice/information,that would help me to accomplish this task? Thanks for the help...
David
David,
You should be able to find pics of a Coiltek adapter that allows one to switch between a coil and a probe. This is basically a small aluminum box with two connectors and a switch that allows the operator to be able to switch between two different style connectors. The small box has a short pigtail that connects the switch box to the detector. By building this box but using the two different connectors needed would allow you to switch between coils having the different connectors. The cable from the small box would then have the appropriate connector to mate to the detector.
This is the technique that would work if you decide you don't want to modify the GS detector. The only problem is trying to find the proper connectors that Eric used. They are difficult to find here in the US. In fact, I never did find the one that fits on the detector. Maybe Eric could help in this respect.
The other alternative would be to change the main connector on the GS to the common 5 pin connector compatible with the TDI. Then you would have to change the connectors on the coils you already have for the GS to the 5 pin types.
That is about the only solutions I can think of.
Reg
You should be able to find pics of a Coiltek adapter that allows one to switch between a coil and a probe. This is basically a small aluminum box with two connectors and a switch that allows the operator to be able to switch between two different style connectors. The small box has a short pigtail that connects the switch box to the detector. By building this box but using the two different connectors needed would allow you to switch between coils having the different connectors. The cable from the small box would then have the appropriate connector to mate to the detector.
This is the technique that would work if you decide you don't want to modify the GS detector. The only problem is trying to find the proper connectors that Eric used. They are difficult to find here in the US. In fact, I never did find the one that fits on the detector. Maybe Eric could help in this respect.
The other alternative would be to change the main connector on the GS to the common 5 pin connector compatible with the TDI. Then you would have to change the connectors on the coils you already have for the GS to the 5 pin types.
That is about the only solutions I can think of.
Reg
LongRanger
New member
Reg,
I believe you have given me the way to deal with my dilemmon. As you are aware,this GS comes with a probe...which,in this case,was no longer working. So,I will take that "port",where I cut off the old probe cord,and mount the TDI connector there. Then,I will simply hit the toggle-switch,for which-ever coil I select.
So,all I need to know,is where to get the connector? Perhaps White's would sell me one? If it's common enough,perhaps right here in Tacoma,or in Olympia.
I certainly do appreciate your in-put here--and feel free to share any of your ideas.
Thanks much,
David
I believe you have given me the way to deal with my dilemmon. As you are aware,this GS comes with a probe...which,in this case,was no longer working. So,I will take that "port",where I cut off the old probe cord,and mount the TDI connector there. Then,I will simply hit the toggle-switch,for which-ever coil I select.
So,all I need to know,is where to get the connector? Perhaps White's would sell me one? If it's common enough,perhaps right here in Tacoma,or in Olympia.
I certainly do appreciate your in-put here--and feel free to share any of your ideas.
Thanks much,
David
The TDI connector is a very common one since it basically is the same as that used on many CB's. So, they can be found at many electronic shops or on Ebay.
So, finding one should be easy.
On a different note, it is hard to believe the probe actually failed. I hope you didn't toss it away since it is possible it might be able to fix it.
Reg
So, finding one should be easy.
On a different note, it is hard to believe the probe actually failed. I hope you didn't toss it away since it is possible it might be able to fix it.
Reg
LongRanger
New member
Reg,
I checked the email that I have posted here,and it looks correct--so I don't know what went hay-wire. That sounds very good,I will check with mouser.
Thanyou very much,
David
I checked the email that I have posted here,and it looks correct--so I don't know what went hay-wire. That sounds very good,I will check with mouser.
Thanyou very much,
David
LongRanger
New member
Yes,I have two very good electronics stores in my area--and I will take my detector into the store--and if they don't have it in stock,they will order it for me.
Thanks again,
David
Thanks again,
David
LongRanger
New member
Reg,
I over-looked the probe part of your reply. I think I may have messed up the probe when I took it apart. But,I think it was kilt anyhow. I plan to use my Falcon Gold Tracker MD20,for my probe. I may try to repair the other one,some-where along the line.
Thanks,
David
I over-looked the probe part of your reply. I think I may have messed up the probe when I took it apart. But,I think it was kilt anyhow. I plan to use my Falcon Gold Tracker MD20,for my probe. I may try to repair the other one,some-where along the line.
Thanks,
David